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  •    Left atrial epicardial fat is a predictor of AF burden
    Siva Soma MD, Allegheny General Hospital, Pittsburgh, PA.

    Atrial fibrillation (AF) remains one of the most common cardiac arrhythmias affecting approximately 2.2 million Americans and many more worldwide, with this number only bound to grow exponentially in the coming decade. While there is ongoing research in identifying prognostic and therapeutic strategies to deal AF, it still remains a formidable challenge to uniformly treat all these patients for the practicing physician.

    A relationship has been described between obesity, epi/pericardial fat, inflammatory cytokine release from perivascular adipocytes, and coronary atherosclerosis. Obesity is also a risk factor for AF and has been associated with pericardial fat. Biopsies from left atrium (LA) in patients with AF have shown evidence of inflammatory cells in the atrial tissue. The authors hypothesized that there might a potential role of periatrial/epicardial fat in AF.

    To test the hypothesis they retrospectively analyzed date from 169 patients undergoing cardiac computed tomography (CT) angiograms for pulmonary vein isolation (PVI) before AF ablation (n=95) and coronary artery disease (CAD; n=74). Patients were categorized according to their highest AF burden: no history of AF, paroxysmal AF and persistent AF. The periatrial epicardial fat thickness was measured at 3 anatomic landmarks: esophagus (LA-ESO), main pulmonary artery (LA-PA), and descending thoracic aorta (LA-TA). LA-ESO fat was found to be thicker in patients with persistent AF versus paroxysmal AF (P=0.011) or no AF (P=0.003). Though LA area was larger in patients with persistent AF than paroxysmal AF (P=0.004) or without AF (P=0.001), LA-ESO was still a significant predictor of AF burden even after adjusting for age, body mass index, and LA area (OR, 5.30; 95% CI, 1.39 - 20.24; P=0.015). A propensity score–adjusted multivariable logistic regression that included age, body mass index, LA area, and co morbidities showed that the relationship remained statistically significant (P=0.008).

    Interestingly enough while the periatrial fat thickness was measured at three different levels, the degree of AF correlated only with the LA-ESO and had a trend towards the slightly negative correlation in the other two. The authors hypothesized that this could be because the pulmonary veins are located posteriorly closest to the esophagus and it is well known that most AF foci originate in and around the pulmonary veins; hence possibly contributing to increased fat deposition in this particular area. It has been shown in previous studies that cardiac surgeries associated with posterior percardiectomies have lower incidence of post-op AF. A recent study by Thanassoulis et al showed a positive correlation of AF with pericardial fat as measured by computed tomography (CT)1 and a study by White et al showed that epicardial anterior fat pad retention prevents attenuation of parasympathetic tone after coronary artery bypass surgery but does not reduce post operative atrial fibrillation2, which further strengthens the authors hypothesis. The correlation was still seen after propensity score adjusted for sex, HTN, HPL, DM, CAD, CHF, and hypothyroidism.

    While the authors have uniquely demonstrated the presence of increased periatrial fat deposition at the level of esophagus in patients with persistent AF, this remains only an association and not a cause-effect relationship. The authors used CT as the diagnostic imaging modality as most of these patients were scheduled for a CT to define their pulmonary vein anatomy prior to ablation, but perhaps magnetic resonance imaging may be a better tool to further delineate and define the borders of periatrial fat using T1 and T2 weighted imaging. It must also be taken into consideration that every patients anatomy is different with varying heart anatomical orientation, chamber enlargement/compression and lung parenchyma volume variability (for example in patients with chronic obstructive pulmonary disease) perhaps leading to more variable fat deposition and would hence render it extremely difficult to define universal protocols for which precise level to measure the periatrial fat by computed tomography.

    References:

    1. Batal O, Schoenhagen P, Shao M, Ayyad AE, Van Wagoner DR, Halliburton SS, Tchou PJ, Chung MK. Left atrial epicardial adiposity and atrial fibrillation. Circ Arrhythm Electrophysiol. 2010 Jun 1;3(3):230-6.

    2. Thanassoulis G, Massaro JM, O'Donnell CJ, Hoffmann U, Levy D, Ellinor PT, Wang TJ, Schnabel RB, Vasan RS, Fox CS, Benjamin EJ. Pericardial fat is associated with prevalent atrial fibrillation: the Framingham Heart Study. Circ Arrhythm Electrophysiol. 2010 Aug 1;3(4):345-50.

    3. White CM, Sander S, Coleman CI, Gallagher R, Takata H, Humphrey C, Henyan N, Gillespie EL, Kluger J. Impact of epicardial anterior fat pad retention on postcardiothoracic surgery atrial fibrillation incidence: the AFIST-III Study. J Am Coll Cardiol. 2007 Jan 23;49(3):298-303.


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